1. Field of the Invention
The present invention relates to a device for detecting an occurrence of misfiring in a multicylinder engine.
2. Description of the Related Art
When one of the cylinders in a multicylinder engine misfires, the engine rotational speed drops at the power stroke of the misfiring period and therefore the time required for the crankshaft to turn by a certain crank angle during the power stroke of the misfiring cylinder becomes longer than that of other cylinders.
Therefore, for example, there is known a multicylinder engine where it is determined, for example, that the no. 1 cylinder has misfired when the period required for the crankshaft to turn by a certain crank angle in the power stroke of the no. 1 cylinder becomes longer than that of other cylinders (see Japanese Unexamined Patent Publication (Kokai) No. 62-228929).
However, when a vehicle is decelerating, the time required for the crankshaft to turn by a predetermined crank angle continues to increase, so the time required for the crankshaft to turn by a predetermined angle at a certain cylinder will become longer than that required a other cylinders. If misfiring is determined from when the time required for the crankshaft to turn by a predetermined crank angle in the internal combustion engine becomes longer than that at other cylinders, then it will be erroneously determined that a misfiring has occurred despite no such misfiring having happened. Further, when a vehicle runs over a bumpy road, the ground contact pressure of the drive wheels with the road surface changes. When the ground contact pressure falls, the drive wheels slip and the engine rotational speed rises. Next, when the ground contact pressure rises and the drive wheels grip the road surface, the engine rotational speed falls. At this time, the time required for the crankshaft to turn by a predetermined crank angle at a certain cylinder will become longer, for a while, than that at other cylinders, therefore an erroneous determination will be made that a misfiring has occurred despite no such misfiring having happened.